package kr.hkit.powerjava.chapter23;

class Counter {
	private int value;

	public synchronized void increment() {
		value++;
	}

	public synchronized void decrement() {
		value--;
	}

	public synchronized void prnCounter() {
		System.out.println(value);
	}
}

class SharedThread extends Thread {
	Counter sharedCounter;

	public SharedThread(Counter sharedCounter) {
		this.sharedCounter = sharedCounter;
		start();
	}

	@Override
	public void run() {
		int i = 0;
		while (i < 20000) {
			sharedCounter.increment();// counter의 value 값을 1 증가
			sharedCounter.decrement();// counter의 value 값을 1 감소

			if (i % 40 == 0) {
				sharedCounter.prnCounter();
				try {
					sleep((int) (Math.random() * 2));
				} catch (InterruptedException e) {}
			}
			i++;

		}
	}
}

public class CounterTest {
	public static void main(String[] args) {
		Counter c = new Counter();
		
		new SharedThread(c);
		new SharedThread(c);
		new SharedThread(c);
		new SharedThread(c);
	}
}
